Valve manifold

ABSTRACT

A valve manifold includes a valve body carrying pairs of laterally spaced piston actuated valves controlled by control modules operative to selectively pressurize and exhaust an outlet port connected to a fluid device and configured in groupings permitting varying valve functionalities.

RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 13/425,820 filed onMar. 21, 2012, which is a continuation of U.S. application Ser. No.12/131,092 filed on Jun. 1, 2008, now U.S. Pat. No. 8,177,188 granted onMay 15, 2012, which is a divisional of U.S. application Ser. No.10/223,236 filed on Aug. 19, 2002, now U.S. Pat. No. 7,490,625 grantedon Feb. 17, 2009, which is a continuation-in-part of U.S. applicationSer. No. 09/840,688, filed on Apr. 23, 2001, now U.S. Pat. No. 6,435,010granted on Aug. 20, 2002.

FIELD OF THE INVENTION

The present invention relates to valves for controlling fluid flow, and,in particular, a control valve assembly having valves integrated with avalve manifold for compactly controlling fluid coupled devices.

BACKGROUND OF THE INVENTION

Manufacturers of hydraulic, pneumatic, and containment equipmentcustomarily test the fluid integrity of their components to ensure safeoperation in the field. Standards are generally prescribed for leakagerates at test pressures and times correlated to the desired componentspecifications.

Currently, leak detection systems are an assembly of separate componentshoused in portable test units. Using a myriad of valves and pneumaticlines a component to be tested is attached to the test unit andindependent valves are sequenced to route pressurized fluid, customarilyair, to the component, which is then isolated. The leakage rate at thecomponent is then measured and a part accepted or rejected basedthereon. The multiple valves and lines may be integrated into a portabletest stand for on-site testing. Nonetheless, the pneumatic system isexpansive and cumbersome, with each element posing the potential forassociated malfunction and leaks. Further, automation of a testingprotocol is difficult because of the independent relationship of thecomponents. Where varying test pressures are required for othercomponents, the system must be retrofitted for each such use.

For example, the leak detection apparatus as disclosed in U.S. Pat. No.5,898,105 to Owens references a manually operated systems wherein thetesting procedures is controlled by plural manual valves and associatedconduit occasioning the aforementioned problems and limitations.

Similarly, the hydrostatic testing apparatus as disclosed in U.S. Pat.No. 3,577,768 to Aprill provides a portable unit comprised of aplurality of independent valves and associated lines for conductingtesting on equipment and fluid lines. The valves are manually sequencedfor isolating test components from a single pressure source. U.S. Pat.No. 5,440,918 to Oster also discloses a testing apparatus wherein aplurality of conventional valving and measuring components areindividually fluidly connected.

Remotely controlled leak detection systems, such as disclosed in U.S.Pat. No. 5,557,965 to Fiechtner, have been proposed for monitoringunderground liquid supplies. Such systems, however, also rely on anassembly of separate lines and valves. A similar system is disclosed inU.S. Pat. No. 5,046,519 to Stenstrom et al. U.S. Pat. No. 5,072,621 toHasselmann.

U.S. Pat. No. 5,540,083 to Sato et al. discloses remotely controlledelectromagnetically operated valves for measuring leakage in vessels andparts. Separate valve and hydraulic lines are required.

In an effort to overcome the foregoing limitations, it would bedesirable to provide a portable leakage detection system for testing thefluid integrity of fluid systems and components that include integratedvalving and porting within a compact envelope for automaticallycontrolling a variable testing protocol. The leak detector includes avalve block having internal porting selectively controlled by fouridentical and unique pneumatic poppet valves for pressurizing the testpart, isolating the test part for determining leakage rates withpressure and flow sensors communicating with the porting, and exhaustingthe test line upon completion of the leakage test. The poppet valvesengage valve seats incorporated within the porting. The poppet valvesare actuated by pilot valve pressure acting on a pilot piston to effectclosure of the valve. The sensors interface with a microprocessor forcomparing measurements with the test protocol and indicate pass or failperformance. Upon removal of the pilot valve pressure, the residentpressure in the porting shifts the valve to the open position. The leakdetector includes plural inlets for accommodating variable pressureprotocols. The leak detector thus eliminates the need for external fluidconnections and conduits between the various detector components,eliminates the need for two-way valving actuation, and provides forconnection with external test units with a single, easy to install,pneumatic line.

In another aspect of the invention, the poppet valves may be disposed insets in a valve manifold to simulate conventional valve functionalitieswith a plurality of fluidic devices. For three way valve functionality,a pair of the pitot valves operates in controlled phased opposition toapply and vent pressure to a one way actuator. For four way valvefunctionality, a second set of oppositely configured valve are used forconventional operation of dual controlled devices such as two wayactuators.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention willbecome apparent upon reading the following detailed description taken inconjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a leak detection valve assembly andcontrol module in accordance with an embodiment of the invention;

FIG. 2 is a schematic drawing of a leak detection system incorporatingthe valve assembly of FIG. 1;

FIG. 3 is a top view of the valve assembly;

FIG. 4 is a front view of the valve assembly;

FIG. 5 is a vertical cross sectional view taken along line 5-5 in FIG.3;

FIG. 6 is a vertical cross sectional view taken along line 6-6 in FIG.4;

FIG. 7 is a horizontal cross sectional view taken along line 7-7 in FIG.4;

FIG. 8 is a horizontal cross sectional view taken along line 8-8 in FIG.4;

FIG. 9 is a fragmentary cross sectional view of a unique poppet valveassembly;

FIG. 10 is a schematic diagram of the leak detection system;

FIG. 11 is a truth table for the leak detection system;

FIG. 12 is a schematic diagram for the control system for the leakdetection system;

FIG. 13 is a perspective view of another embodiment of a valve assemblyfor a leak detection system;

FIG. 14 is a perspective view of a valve manifold assembly in accordancewith another embodiment of the invention;

FIG. 15 is a top view of the valve manifold assembly shown in FIG. 14;

FIG. 16 is a front view of the valve manifold assembly shown in FIG. 14;

FIG. 17 is a left end view of the valve manifold assembly shown in FIG.14;

FIG. 18 is a cross sectional view of the valve manifold assembly shownin FIG. 14, with the control module removed and including crosssectional view of valve sets taken along lines A-A and B-B in FIG. 16and a schematic view of the control system for the valve sets for threeway and four way valve functionality;

FIG. 19 is a fragmentary cross sectional view taken along line 19-19 inFIG. 18; and

FIG. 20 is a cross sectional view of a valve manifold according anotherembodiment of the invention illustrating a two way valve functionality.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings for the purpose of describing the preferredembodiment and not for limiting same, FIGS. 1 and 2 illustrate a leakdetection system 10 for determining the pressure integrity of componentswhen subjected to pressure conditions during a test period. The leakdetection system 10 comprises a valve assembly 12 and a control module14 operatively coupled with a flow sensor 16 and pressure sensor 18. Ashereinafter described in detail, the leak detector 10 is operative fortesting the fluid integrity of test parts to determine is leakagestandards are being achieved.

Referring additionally to FIG. 10, the valve assembly 12 is fluidlyconnected with a low pressure source 20 along line 22, a high pressuresource 24 along line 26, a test unit 28 for testing such parts alongline 30, and an exhaust 32 along line 34. Supplemental valves may bedisposed in the lines for controlling flow therethrough.

The control module 14 comprises a pilot valve assembly 36 includingpilot valves 40, 42, 44, and 46 fluidly connected with a high pressurevalve unit 50, a low pressure valve unit 52, an exhaust valve unit 54and an isolation valve unit 56 along lines 60, 62, 64 and 66,respectively. The pressure sensor 18 is coupled with the isolation valveunit 56 by line 68. The flow sensor 16 is connected with the valve unitsat manifold line 70 and with test part line 30 along line 72. The pilotvalves are connected to pilot pressure 74 by manifold line 76. The linesand attendant fittings will vary in accordance with the parts undergoingtesting and the test conditions.

Referring to FIGS. 3 through 8, the valve assembly 12 comprises a valveblock 40 housing via ports to be described below a low pressure valveunit 80, a high pressure valve unit 82, an exhaust valve unit 84 and anisolation valve unit 86.

As shown in FIGS. 5 and 8, the low pressure valve unit 80 is fluidlyconnected with line 28 and low pressure source 20 by a low pressureinlet port 90 intersecting with a vertical cross port 92. The highpressure valve unit 82 is fluidly connected with line 26 and highpressure source 24 by a high pressure inlet port 94 intersecting with avertical cross port 96. As shown in FIG. 6, the isolation valve unit 86is fluidly connected with the line 30 by the isolation port 98 andvertical port 99. The exhaust valve unit 84 is fluidly connected withline 32 by exhaust port 100. As shown in FIG. 4, the ports 90, 94 and100 are disposed on the front face 102 of the valve block 12. Theisolation port 98 is disposed on the rear face 104 of the valve block12. The ports 100 and 98 are located laterally in a central verticalplane. The ports 90 and 94 are symmetrically disposed on opposite sidesof the exhaust port 100 and therebelow. The ports 100, 94 and 90 lie ina common horizontal plane. Each of the ports is provided with an outerthreaded bore for connection to the associated lines with an appropriatefitting for the fluid application.

All of the valve units have a common architecture as representativelyshown in FIG. 9. Therein, a valve unit 110 including a poppet 112 havinga valve stem 113 supported by sealing disk 114 for reciprocation betweena raised vent position as illustrated and a lowered sealed position incounterbore 115. The poppet 112 includes a cylindrical valve body 116carrying 0-ring 117 that engages the annular valve seat 118 ofcounterbore 115 formed coaxially with a vertical port 120. The outer rimof the sealing disk 114 is supported at the base of a secondarycounterbore vertically above bore 115. The secondary counterboreoutwardly terminates at an internally threaded end. A vent cap 124includes a cylindrical sleeve 125 threadedly received in the threadedbore and a circular base 126 having a threaded center hole 128. Anactuating piston 129 including 0-ring 130 is axially slidably carried atthe interior surface of the sleeve of the vent cap 124 for movementbetween a raised position engaging the base 128 and a lowered positionengaging the top of the valve stem 113 for moving the poppet 112 to thesealed condition. Angularly disposed vent holes 131 are formed in thesleeve 125 for venting the piston. An air line connected with the pilotpressure line is connected at the center hole 128 for connection withthe pilot pressure control system.

In typical operation, when pilot pressure is applied in the chamberabove the piston 129, the piston 129 is forced downwardly therebyshifting the poppet 112 to the sealed position. When the pilot pressureis removed and the port 120 is pressurized, the poppet 112 and thepiston 129 are driven to the raised, open position. Assist springs maybe deployed, particularly in the isolation valve, for providingadditional biasing to the open condition.

As shown in FIGS. 5 through 8, with respect to the exhaust port 100 andvalve unit 84, a counterbore 138 is formed in the bottom surface of thevalve block 40 coaxially therewith. A circular sealing blank 140 isretained at a step in the counterbore 138 by a split retaining ring 142retained in a corresponding annular groove thus defining a pressurechamber 144. A C-shaped distribution channel or port 150 extends fromthe chamber 144 upwardly and intersects the counterbores 115 of valveunits 110.

Accordingly, when either of the pressure valve units is pressurized fromits source and the pilot control to the piston is interrupted, the airflow in the ports 92, 96, 99 shifts the poppets to raised, openpositions, thereby pressurizing the distribution port 150 and chamber144 resulting in pressure communication therebetween. Referring to FIGS.3, 7 and 8, a pair of vertical ports 160 communicate upstream of theisolation valve unit 84 for connecting one line of the flow sensor 16and the pressure sensor 18. A pair of vertical ports 162 communicates onthe other side of the isolation valve units 84 with the distributionport 150. Accordingly, the flow sensor 16 in a conventional mannermeasures pressure transients on the part under leakage test while thepressure sensor 18 measures pressure conditions on both sides of theisolation valve.

The valve unit is operationally connected to an independent test unitwhereat parts to be leak tested may be deployed. The test protocol mayspecify a high pressure test for a defined test period or a low pressuretest for a defined test period. Test parts are deemed successful if theleakage under pressure as determined by the flow sensor 16 is below apredetermined threshold. The control system 14 is effective forestablishing the appropriate protocol.

Referring to FIG. 12, the control system 14 comprises the pilot valvesystem 250, a microprocessor 254 coupled with a control panel 255 fordefining and conducting the test protocol, test result indicator lights256 a display screen 257, for denoting passing or failing of the testconnected to a suitable power supply 258. The microprocessor 254contains the protocols for the various parts, preferably programmedthrough an external computer port 260. The desired protocol is accessedat control panel 255 through menu button 264, start button 266 andscroll buttons 268.

The operation of the leak detector is illustrated in the truth table ofFIG. 11 and taken in conjunction with the schematic of FIG. 2.

A part to be tested in mounted in the test fixture, the control systeminitialized and the test protocol selected. Thereafter, the test isinitiated by actuating the start button 266. As a first condition, thehigh and low pressure lines are pressurized with the accompanying pilotvalves 40, 42 in the normally open positions with the solenoidsdeenergized. This applies pilot pressure to the associated poppets toclose and seal the high pressure and low pressure valve units 50, 52.Correspondingly, the normally closed exhaust pilot is deenergized andthe exhaust valve 54 is in the open position. The normally closedisolation pilot is deenergized and the isolation valve unit 56 is in theopen position.

Thereafter the high pressure pilot 40 is energized, venting the highpressure poppet whereby inlet high pressure air raises the high pressurevalve unit 50 to the open position. Concurrently, the exhaust solenoidis energized admitting pilot pressure to the exhaust poppet pistonchamber and shifting the exhaust valve unit 54 to the closed positionand air flowing past the high pressure poppet pressurizes the exhaustchamber 144 through the distribution channel and past the isolationvalve unit 56 to pressurize the test part with high pressure air.Thereafter, the isolation pilot is energized applying pilot pressure tothe isolation piston chamber and closing the isolation poppet.Thereafter, the flow sensor 16 monitors pressure transients and throughthe microprocessor interface denotes pass or fail conditions at theindicator lights.

Upon completion of the test, the isolation pilot solenoid is deenergizedpressurizing the high pressure piston and sealing the high pressurevalve seat, thereby ceasing inlet flow. Concurrently, the isolation andexhaust pilot solenoids are deenergized allowing exhaust chamber andpart pressure to shift the exhaust and isolation valves to the openposition for completion of the test. In the event of excessive pressurelost at the test part, a light biasing spring may be provided at theisolation poppet to ensure movement to the open position.

For testing under low pressure conditions, the exhaust poppet is closedand the low pressure valving sequenced in similar fashion to the highpressure test detailed above. More particularly, a part to be tested inmounted in the test fixture, the control system initialized and the testprotocol selected. Thereafter, the test is initiated by actuating thestart button 266. As a first condition, the high and low pressure linesare pressurized with the accompanying pilot valves in the normally openpositions with the solenoids deenergized. This applies pilot pressure tothe associated poppets to close and seal the later. Correspondingly, thenormally closed exhaust pilot is deenergized and the exhaust poppet isin the open position. The normally closed isolation pilot is denergizedand the isolation poppet is in the open position.

Thereafter the low pressure pilot 42 is energized, venting the lowpressure valve whereby inlet low pressure air raises the low pressurevalve unit 52 to the open position. Concurrently, the exhaust pilot isenergized admitting pilot pressure to the exhaust poppet piston chamberand shifting the exhaust valve unit 54 to the closed position and airflowing past the low pressure poppet pressurizes the exhaust chamberthrough the distribution channel 150 and past the isolation poppet topressurize the test part with high pressure air. Thereafter, theisolation pilot solenoid is energized applying pilot pressure to theisolation piston chamber and closing the isolation poppet. Thereafter,the flow sensor monitors pressure transients and through themicroprocessor interface denotes pass or fail conditions at theindicator. Upon completion of the test, the isolation pilot isdeenergized pressurizing the low pressure piston and sealing the lowpressure valve seat, thereby ceasing inlet flow. Concurrently, theisolation and exhaust pilot solenoids are deenergized allow exhaustchamber and part pressure to shift the exhaust and isolation poppets tothe open position for completion of the test.

Referring to FIG. 13, a fully integrated package is illustrated for aleak detection valve 280 as described above. The valve 280 comprises anextruded metallic valve body 282 having four valve assemblies 284, asdescribed above. The valve assemblies are controlled by solenoids 286carried on a top horizontal surface. The valve body 280 has an isolationport 288 in the illustrated rear wall thereof, and high and low pressureports, and an exhaust port in the front wall thereof, which are notshown and function as above described. The control lines for the valveassemblies 284 are routed through a distribution bracket 290. Theinterior pressure sensors are coupled at pin connector 292 on the topsurface of the valve body 280 for operative connection to associatedinstrumentation.

Referring to FIGS. 14 through 17, in another embodiment of the inventionthe valving is incorporated into a control valve manifold 300. Themanifold 300 includes an extruded lower valve body 302 carrying on a topsurface a plurality of longitudinally spaced control modules 304 foroperatively controlling conventional fluidic devices, not shown, coupledat a longitudinal series of associated outlet ports 306 exiting at alongitudinal side wall of the valve body. An inlet port 310 and anexhaust port 312 extend longitudinally through the valve body 302 inparallel spaced relationship for interconnection with the valving asdescribed in greater detail below.

The ports 310 and 312 terminate at internally threaded ends. At theremote end, the ports are suitably sealed with a stop member, such as athreaded plug (not shown), or coupled with a succeeding manifold. Theinlet port 310 is coupled with a supply line for supplying inlet fluidunder pressure for control by the valving and controlled operation ofthe associated fluidic devices. The exhaust port 312 is coupled with anexhaust line for routing to an appropriate location the exhaust fluid.

A pair of upwardly opening laterally spaced longitudinal channels 320are formed in the top surface of the valve body 302. Solenoids 322 arecarried in the channels 320 and operatively associated with the controlmodules 304 for controlling pilot pressure to the valving at pilot lines324. The modules 304 are connected to a suitable power source viamultiple-pin socket connector 326 carried on the front lateral side wallof the valve body 302. The valve modules 304 control the flow betweenthe ports 310, 312 and the operative outlet ports 306 of the manifold300. If certain of the ports are not required for an application, theoutlet ports may be plugged or capped, and additionally the associatedcontrol module deleted. Any ports associated with the inactive outletports are also deleted or plugged.

It will also be apparent that the length of the valve body may betailored to the devices to be controlled and may be coupled in series orparallel with other valving manifolds.

The manifold in controlled formats may be advantageously employed toreplicate the functionality of various conventional valvingconfigurations, such as two-way, three-way, four-way, five-way valves.In such configurations, the manifold operates with lower controlpressures within a substantially smaller envelope.

More particularly, as shown in FIG. 1-8, each control module 304 isassociated with a pair of laterally spaced valves 340, 342 in Valve Aand valves 344 and 346 in Valve B. The valves are operatively disposedin the valve body 302 as referenced in FIG. 9 above.

The inlet valves 340, 344 are disposed in upwardly opening verticalbores in the valve body normal to the inlet port 310. Each valveincludes a slidably stem supported inlet valve member 360 downwardlymoveable by a floating piston 362 from a raised position communicatingwith the inlet port 310 and a closed position engaging an annular valveseat downstream of the inlet port.

The exhaust valves 342, 346 are disposed in upwardly opening verticalbodes in the valve body normal to the exhaust port 312. Each valveincludes a slidably stem supported outlet valve member 370 downwardlymoveable by a floating piston 372 from a lowered position engaging anannular valve seat upstream of the exhaust port 312 and a raisedposition communicating with the exhaust port.

An exhaust plenum chamber 380 is formed in the valve body 302 below theexhaust valve seat and in the open position communicates with theexhaust port. The exhaust plenum chamber 380 is sealed by a circularcover member 382 and sealed as described with reference to the priorembodiment. Referring to FIG. 19, a cross passage 384 is formed at theouter periphery of the exhaust plenum chamber and established a fluidpath extending serially from the outlet port 306 to the cross passage tothe exhaust plenum chamber 380 to the exhaust port.

Each piston is carried in a valve cap threadedly connected in a boreextending from the top surface of the valve body coaxial with theexhaust valve seat. The valve caps are fluidly connected with branchpilot lines 323 above the piston.

Referring to Valve A in FIG. 18 illustrating a three way valvefunctionality, the exhaust valve 370 is connected at the branch pilotline with a normally open solenoid valve 400 connected with the mainpilot line 402. The inlet valve 360 is connected at the branch pilotline with a normally closed solenoid valve 404 connected with the mainpilot line.

The outlet port 306 is formed in the side of the valve body 302 andintersects the inlet valve bore above the inlet valve seat. The deviceport is fluidly connected by line to one side of a single actingactuator 410, including return spring biased piston 411, by lines 412and 414.

In operation, the inlet valve member 360 is moved upwardly to an openposition by inlet pressure on the lower surface thereby shifting thepiston to a raised position, establishing a fluid path through outletport 306 and lines 412, 414 and extending actuator piston 411. Theoutlet valve member is shifted by the piston to the closed positionsealing flow to the outlet port. To retract the piston, the solenoidvalves are reversed, whereby the inlet valve member 360 is closed, theoutlet pilot pressure removed allowing pressure conditions in the plenum380 to move the exhaust valve member 370 to the open position andventing the actuator to the exhaust port 312 thereby retracting theactuator piston under the spring biasing.

For four way simulation according to the invention, Valve B isoperatively coupled with Valve A. Valve B has a normally open inletsolenoid valve 420 and a normally closed exhaust solenoid valve 422.Valve A is coupled with one end of a double acting actuator 430,including piston 431, by lines 412, 432. Valve B is couple at the outletport with the other end of the actuator 430 by line 434.

In operation, the extension of actuator is controlled by Valve A asabove described, and Valve B is in the exhaust mode. To retract theactuator piston 431, Valve A is conditioned for exhaust and Valve B isconditioned for pressure, thereby shifting the piston 431 to theretracted position.

Referring to FIG. 20, the valve manifold of the present invention mayalso provide two way valve functionality. Therein, a valve 500 includesa valve body 502 carrying a valve assembly 504 as described above. Theinlet valve member 506 is moved by piston 508 under pilot conditionscontrolled by normally open solenoid valve 510 between a lower closedposition engaging the inlet valve seat and the illustrated raised openposition. In the open position with the solenoid valve vented, the valvepermits fluid flow from supply line 520 to inlet port 522 past valvemember 506 to outlet port 524 to a pressure dependent device 526. Uponreversal of the solenoid valve 510, the pilot pressure is applied to thepiston to closed the valve member and block flow therethrough. At thenext actuation, the inlet pressure shifts the valve member to the opencondition.

With the above constructions, it will be appreciated that the individualvalve members may be independently controlled and sequenced to a desiredactuation schedule. In particular for spool valve simulation, the normalcrossover time between valve positions may be eliminated by concurrentactuation of the solenoids. Should staged actuation be desired, timesequencing may be used. Further the valve ports may be integrated withother flow control. Each such simulation provides the compact sizeafforded by the valves directly place in the manifold bodies, and thelow pilot pressures required by the valves, as well as the valve openingpressures afforded by resident pressurization.

Having thus described a presently preferred embodiment of the presentinvention, it will now be appreciated that the objects of the inventionhave been fully achieved, and it will be understood by those skilled inthe art that many changes in construction and widely differingembodiments and applications of the invention will suggest themselveswithout departing from the sprit and scope of the present invention. Thedisclosures and description herein are intended to be illustrative andare not in any sense limiting of the invention, which is defined solelyin accordance with the following claims.

The invention claimed is:
 1. A valve assembly, comprising: a valvehousing including a bore including an upper end, a lower end and anintermediate annular valve seat; a low pressure inlet port and a highpressure inlet port; a valve member slidably carried by a sealing disksealing the bore and moveable between a closed position engaging thevalve seat and blocking fluid flow through a vertical port and an openposition permitting fluid flow through the vertical port, wherein thevalve member includes a poppet having a valve stem; a piston memberhaving a surface slidably carried in the bore for moving the valvemember to the closed position under pressurized conditions, wherein anend of the valve stem is engageable with the surface of the pistonmember; and a control for selectively applying pressurized conditions tothe piston member for effecting the closed position and reverselyconditioned for removing the pressurized conditions and permit movementof the valve member to the open position by pressure conditions in thelower end of the bore, thereby providing two way valve functionality. 2.The valve assembly as recited in claim 1 wherein the valve stem isreceived in an opening in the sealing disk and is supported by thesealing disk.
 3. The valve assembly as recited in claim 1 wherein thevalve seat is coaxial with the vertical port.
 4. The valve assembly asrecited in claim 1 wherein, when pilot pressure is applied, the pistonmember moves and the valve member shifts to the closed position.
 5. Thevalve assembly as recited in claim 1 wherein, when pilot pressure isremoved, the piston member moves and the valve member shifts to the openposition.
 6. The valve assembly as recited in claim 1 wherein there arefour valve housings, and a low pressure valve unit is fluidly connectedby the low pressure inlet port by a first line to a low pressure source,a high pressure valve unit is fluidly connected by the high pressureinlet port by a second line to a high pressure source, an exhaust valveunit is fluidly connected by an exhaust port by a third line to anexhaust, and an isolation valve unit is fluidly connected by anisolation port by a fourth line to a test unit.
 7. The valve assembly asrecited in claim 1 wherein the piston member and the valve member areseparate components.
 8. The valve assembly as recited in claim 1 whereinthe valve housing includes a first portion and a second portion attachedto the first portion, wherein the first portion and the second portionenclose the valve member and the piston member.
 9. The valve assembly asrecited in claim 8 wherein the first portion includes an externallythreaded portion and the second portion includes an internally threadedportion that engages the externally threaded portion of the firstportion to define the valve housing.
 10. The valve assembly as recitedin claim 8 wherein the first portion of the valve housing includes anangularly disposed vent hole.
 11. The valve assembly as recited in claim8 wherein an outer rim of the sealing disk is located between the firstportion and the second portion of the valve housing.
 12. The valveassembly as recited in claim 8 wherein the piston member is located inthe first portion of the valve housing, and a seal located between thepiston member and the first portion of the valve housing is slidablycarried on an interior surface of the first portion of the valve housingduring movement of the piston member in the first portion of the valvemember.
 13. The valve assembly as recited in claim 1 wherein a flatsurface surrounding the vertical port defines the valve seat.
 14. Thevalve assembly as recited in claim 1 wherein a seal is located betweenthe valve stem and the cover.
 15. The valve assembly as recited in claim1 wherein the piston member, the valve member, and the cover areseparate components.